The present invention relates to an insertion unit for an endoscope accommodating a plurality of components such as tubes and bundles of optical fibers.
An endoscope has an insertion unit which is to be inserted into a human cavity. The insertion unit generally includes a flexible tube provided at a distal end portion thereof. Generally, the flexible tube is bendable by operation at an operation unit formed at a proximal end portion of the endoscope. Inside the flexible tube, a plurality of components such as tubes and bundles of optical fivers are accommodated.
The flexible tube is configured such that the diameter thereof is as small as possible so as not to provide much pain to a patient during an endoscopic inspection. On the other hand, the diameter of the flexible tube is also determined to have its minimum diameter at which the components inside the flexible tube will not crush each other.
Conventionally, the minimum diameter is determined such that the following condition is satisfied.
Σs/S falls within a range of 0.7-0.8, wherein Σs is the sum of cross-sectional areas of the components inside the flexible tube, while S represents the inner cross-sectional area of the flexible tube.
In the conventional insertion unit configured as above, when the flexible tube is repeatedly bent, the bundles of optical fibers may meander inside the flexible tube and/or may be stretched. In particular, when the optical fibers are stretched, they may be gradually broken and the amount of light for illuminating an object to be observed is lowered. It is generally said that if a rate of damaged optical fibers reaches 10%, the reduction of illumination light affects the observation performance, and that if the rate of damaged optical fibers exceeds 20%, the observation performance will be significantly damaged.